The present invention is directed to a device for processing a corrugated board web having a core web of preglued corrugations with upper and lower cover paper webs secured to the corrugations of the core web. The device includes at least one lower heating plate, a pressure belt disposed above the plate to form a path for receiving the corrugated board web moving in a first direction at a first linear speed with the belt moving with the same linear speed as the corrugated board web and pressing the upper paper web against the core web, and means acting on the pressure belt to load the belt.
In common practice, such devices are used in the heating section of a so-called double-facing station of a corrugated board manufacturing machine. In this station of the machine, the corrugated board, which is made up by the glue assembly consisting of lower and upper smooth cover paper webs as well as of a corrugated web is subjected to a heating process which is to ensure the definite gluing and the drying of the various webs. This heating process usually occurs with the corrugated board web travelling onto a series of heating plates, which are made out of cast iron or steel and are heated with steam which circulates within the heating plates.
An endless pressure belt, whose lower run is pressed onto the upper cover paper web of the corrugated board web, keeps the corrugated board web in contact with the heating plates. The pressure rate of the pressure belt is amplified by free rotating rollers which are arranged in grooves or on pivoting levers in such a way that they may rest on the pressure belt that is to ensure therewith a distribution, at least approximately, of their weight on the corrugated board web. To perfect the contact pressure of the corrugated board on the heating plates, each roller supporting element is associated with a jack provided with fluid under pressure, which system allows the modification of the speed of the thermic transmission between the heating plates and the corrugated board web, when the pressure contact is changed. Such a device is described in French Document No. 1,592,115.
The main drawback with such a device remains in the fact that it is difficult, if not risky, to adjust the pressure exerted by the rollers on the belt with the thermic transmission speed selected so as to obtain an appropriate drying process which shall not deform to an unacceptable extent the corrugated board web by more or less flattening the corrugations of the web.
In order to avoid this phenomenon, it has been provided to replace the rollers with a series of pressure boxes provided with compressed air. The pressure exerted by the compressed air of the boxes presses the pressure belt onto the corrugated board web with a uniform rate, thus allowing the setting of the pressure by making the air pressure vary in the different boxes. U.S. Pat. No. 4,947,559, whose disclosure is incorporated herein by reference thereto, discloses such a device.
In this field, the professionals are always aware of another device that also makes use of pressure boxes in which a movable plate has been arranged which closed almost the whole lower part of the box in such a way that the pressure is transmitted mechanically onto the pressure belt in order to keep a better distribution of the pressure on the belt.
As already mentioned, the use of rollers and jacks that apply the pressure stress transmitted onto the pressure belt causes deformation of the corrugated board web. However, this solution permits the removal of humidity resulting from the steaming of the water residing in the glue which will have served for the assembly of the various paper webs making up the corrugated board web. This removal is an absolute necessity for obtaining corrugated board webs of an acceptable quality.
The other two above-described devices have non-neglectable advantages with regard to the impossible deformation of the corrugated board, but interfere at a large rate with the removal of the humidity, which fact is unacceptable for the manufacture of high-quality corrugated board.